Commons diversity measures urged
Parliamentary candidates should have a legal right to time off work to campaign, and parties should offer bursaries to would-be MPs from poorer backgrounds, a think tank says.
The Institute for Government said Westminster was "overwhelmingly white, male and middle-class".
Just one fifth of MPs are women, and 27 out of 650 are from ethnic minorities.
The cost and time involved could deter "candidates from non-traditional backgrounds", the organisation said.
The report acknowledged parties' past diversity efforts, including all-women shortlists by Labour and the Conservatives' "A-list" of approved candidates.
But the Institute for Government argued that improved selection methods were "only part of the answer".
"The problem is increasingly not overt or covert discrimination within political parties, but the lack of women applying to become candidates in the first place. The same is true for other under-represented groups," the report said.
It went on: "Parties need to focus on increasing the supply of aspiring parliamentary candidates by removing some of the barriers to participation, including the high cost and time commitments, which act as a significant deterrent to candidates from non-traditional backgrounds.
"Childcare costs mean that this can be a particular barrier for women, while disabled candidates also often face extra costs."
The report cited examples of one MP who had sold her house "in order to get elected", while another candidate had been left so badly in debt after a failed campaign that she could no longer afford to attend the party conference.
"Parties have to open their doors more widely and diversify the ways in which people can become involved in their activities," said report co-author Rhys Williams.
"It will only be through bold action that the problems of low public participation in the political process and an unrepresentative Parliament can be addressed."